Call-distributing telephone-exchange system.



S. H. BROWNB.

Patented July 6, 1909.

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CALL DISTRIBUTING TELEPHONE EXCHANGE SYSTEM. APPLICATION FILED 123.11,1905. RENEWED 0013.25, 1907.

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UNITED STATES PATENT OFFICE.

SIDNEY vHAND BROWNE, OF PITTSDURG, PENNSYLVANIA, ASSIGNOR TO lMERICAN'lE-LE- PHONE AND TELEGRAPH COMPANY, A CORPORATION NEW YORK.

CALL-DISTRIBUTING TELEPHONE-EXCHANGE SYSTEM.

Specification of Letters Patent.

Patented July 6, 1909.

application filed February 11, 1906, Serial No. 255,216. Renewed October25, 1907. Serial No. 399,195.

telephone exchange systems.

In the general system, for which the improvements constituting mypresent inven-, tionare particularly designed, the entire ex change maybe said to be built up of two classes of units, line units and trunkunits.

Eachline unit consists of a telephone line having'at itssubstation endatelephone, and at its central office end two switching olements which Iwill designate respectively as a connecting element. and a callreceivingelement. The connecting element is an automatic switchwhich-isthrown intormove ment by the removal of thesubstation telephone receivedand: travels consecutively over waiting contacts of: a plurality oftrunkswhich it testsuntilit arrives-at the contactsof 'a trunk notalready in use; upon finding suchanon-busy trunk, the automaticswitchconnects its line with that trunk and main-- tainst'heconnectionuntilithe hanging u of the receiver at the calling SUbSliiLlilOIl. Thecall receiving element at the central office and of the telephone lineconsists of switch-- boardl jacks, one at each section of. theswitchboard. Each trunk. unitconsists genmay of'a speech: transmittingportion terminating at one end in Waiting contacts, which latteraremultipled to the automatic switches of a plurality of telephonelines; said'trunkunit terminates at its other end in a connectingelement consistin of a plugadaptcd to be insortedin alswitc Board jackat the called telephone line. A: central operators telehone bus testconnections whereby th switchboard jacks of engaged telephone linesafford a busy signalnwhcn tested with a trunk. plug, and; supervisorysignaling means, are provided. It willitherefoie be understoodthat insuch a s stem the removal of the-"receiver at'a. telep one sub stationoriginates a; call; that in. response'to this removal: ofI-the receiverthe automatic switch of said telephone line will. automatically connectthe line with a disengaged trunk;that an operator in attendance upon.

thattrunk takes the calling subscribcrs order 1n the usual. way andthereupon (0111- pletes the connection by inserting the trunk plug in aswitchboard jack of the called telephone line.

The improvements constituting my presout inventionrclate particularly tothe construction, combinations and arrangements of apparatus andcircuits (particularly at the central oflicc) of systems such asoutlined above, with-the object'of affording maximum efficiency ofoperation under the varying and, exacting conditions of commercialtelephonic service. These improvements may be read.- ily understood fromthe detailed description which follows, wherein reference is made totheaccompanying drawing illustrating what I believe to bethe preferredembodiment of the invention.

Referring to the drawing, and in order toafford at the outset a generalidea of the structure illustrated, aline unit is shown (at the left) theprinc-i al parts thereof being the telephone line COIN uctors 18,substation telephone 19, switchboard jacks 20 connected inmultiple, andautomatic switch 1 0; with these parts there are associated various.relays, resistances, circuits and connections (shown at the left-handside of the drawing) fully explained hereafter. The battery 47 and.interrupter 15 are common to all lines terminating at'the-centralpllicc. A trunk unit (shown between the line unit at the left andanother line unit at the extreme right) has as its principal parts,waiting contacts 31,- 32 and 33 of switch 10, and similar contacts atother similar switches of'other lines, a plug-'30, and conductorsleading from the plug to the-waiting contacts; with these parts areassociated various relays, lamps, keys, condensers, and circuitconnections, all fully explained hereafter. signal generator 122 arecommon to all of the trunksof the exchange.

The mechanical details of the automatic switch 1.0 need form. no part ofthe presentinvention, and'hence general reference there to willsiiflice. There are upon the market many forms of stepby-s'tep switches,and some forms of continuous-motion switches,

in which movable terminals are propelled. from contact to contact, orfrom set to set of.

Battery 47 and call ion 7 mg contacts of which one, set is shown at 1contacts.

.located individual contacts of the fixed set reached, there being'aplurality of fixed sets waiting to'be wiped over by the-movable Fromthis relation existing between the fixed and movable contacts, the tern1wiperis. a convenient one for' the movable terminals and theterm waitincontacts is a convenient one for the fixe points. In such switches anelectromagnet moves the wipers or causes them to be moved and anotherelectromagnct restores them or causes them to assume their, originalposition v phone line 18, having its win lng connected of rest. p Theautomatic'electric switch shown at 10 consists of shaft 11 under tensionof volute sprin 12, adapted to be advanced step b step t. rough an angleof one step upon eac energization of magnet 13 and to be returned to itsposition of rest, 11 on the energization of magnet 14;' The shat11,carries a set of three wipers 21-22- 23, and the frame of the switchcarries a pluralityof sets of wait- 31-3233. Aninterrupter 15 is shownin the circuit of magnet 13; the purpose of the interrupter bein toalternately denergize and renergize t e magnet 13" when the circuitthrough that magnet is closed at all other oints, thus, propelling theshaft 11' throug successive steps. Pin 16. attached to a moving part oftheautomatic switch enga es one member of the electrical switch 17 anseparates the two. members in that switch when the shaft 11 and othermoving parts are in their normal o'sitions of rest (as shown in thedrawing), t e switch 17 bein closed at the first step of the moving partan remaining closed until broken by the restoretion of the switch tonormal. v H To the waiting contacts 31-32.33, are connected conductors41-42-43 havin a trunkequipment as shown, and having a so extensions51-52--53 reaching to-sets of waiting contacts (similar to313233),ofother automatic switches similar to that herein described,but servingother tele hone aving a lines, thus making each trunk accessib e to aplurality of tele hone lines in addition to Iplurality of trunksaccessible to each telep one line.

I .20 are multiple switchboard jacks for tele phone line 18, one'ackbein located at eachsection of-the multiple switc board.- 20' are 1similar jacks for telephone line 18'. One

conductor-of telephone line; 1-8-leads to an armature ,49 normallyresting 1a ainstits back contact connected to groun by conductonLOO. Theother conductor of=said line leads through a resistance 29 to armature48 whichnormally rests againstits back" conductor 69 branchi leads tomechanism 0 the trunk, as hereafconductors oftele hone line 18 havesimilar connections; one eads to an armature 49 which normally restsagainst its back contact, and from the latter a conductor (not shown)leads to ground; the other leads through a.

resistance 29 to-armature 48 which normally rests against its backcontact, and a shunt connection 101 around resistance 29 includes thewinding of 'a line relay 26. A conductor 102 leads from the frontcontact of armature 49 to Wiper 21, and a conductor 103 leads from frontcontact of armature 48 to wiper 22. I

27 1s a cut-ofi and connectin relay for telein a-conductor 63'leadingfrom the sleeve away from their back contacts into engagement with theirfront contacts. 27 is a similar cut-ofi and connecting relay fortelephone line 18 conductor 63 leads from the sleeve contacts of jacks20 to one end of the winding of said relay, while a conductor 106 leadsfrom the other end of' said Winding to ground at battery 47.

from their back contacts into engagement with their front contacts. Arelay 25 has its 'winding connected in a conductor 107 which leads fromthe back contact of armature 48.

toone pole of the common battery 47, the other pole of which isconnected to ground by conductor 108. A branch 109 from conductor 107leads to an armature 50, norma1ly retracted from en a ement with itsfront contact, from which atter a conductor 110 leads to an armature 54which normally e11- ages its back contact. A conductor 111 eads from thelatter through the winding of magnet 13, and interrupter 15 to conductor106. A branch 112 leads from conductor 107 toan armature59 of relay 26,normally retracted against its back contact, from which'latter aconductor 78 leads through the windings of magnet 14 to the movablemember of switch 17. Conductor 79 leads from the fixed member or backcontact of said switch to conductor 106.- A conductor 60, erforming'important functions'in connectlon with the present invent on, leads fromthe front contact of armature 59 to the front contact of an armature 58of a testing and connecting relay 24; from said armature 58, conductor61 leads through one winding of 'relav' 24 to a resistance 28, and fromthe latter-by conductor 62 to conductor 63. A from conductor 107,

ter explaineth A. branch conductor 55 from conductor 69 .l eadsthrough'a second winding of relay 24 testing-wiper 23.v

(includes the winding of a line relay 26. v The 1 Relay 27 when en- Iergized attracts its armaturcs 48, 49, away- 71 of a relay10,thisconnectionforminge11 important part of the presentinvention-byfully explained here- Another conductor 57 leads homer mature 56 throughone winding of relay 37 to conductor 106. 'Arma-ture 56 isvnormsllyrea4.6 tofa' secondifront contact of armature 71 end of the telephone line19, I will next explain the circuit vcormections and-nmeclnmism of thecentral station trunks-,only one of which is shown in the drawing. Fromwaitterminel of the. trunk, as, it may be called, conductor 43 lends ingcontact 33, orthe testi rele'y37', armature and to one of' two frontcontacts of an,-'zarmature reason of its functions after.

tracted into engagement with. its backgjco'nfe' tact and out o,engagement with its' -fiontj contact; from theflatter, conductor {68-leade Y through aseeond winding of 'rela.

front contact of an armature 67 w i'ch is normally retracted fromengagement said contact, and from said armature a conductor 113 leadsto'eonductor 69.. "A branch 53 f-romconductort 43, leads to waitingcontacts 33 of the automatic switchesjof other telee phone lines. 7 Fromthe waitingcontact 3 2, a conductor 42 leads through a condenser36'to acontact 114 of e key 34. A branch [85,

from conductor 42,1eads' through oneof two windings of a relay338 toconductor69. A

branch 52, from conductor 42,-leads to wait irigl contacts 32 of theeutometic-switches of 0 l or telephone .lines. Branch 73 from conductor42 leads-through one oftwo'windings of a relay 39 to conductor 69. -From thi waitin contect 31, conductor 411 leads throu 34. ranch 83 .leadsfrom conductor 41 through a second winding of relay 38 to-con ductor106; .Branch 51 from'conductor 41 leads to'wnitin contacts 31 ofthesutomat'ic switches of ot 'er telephone lines; Branch 76 from conductorMilecds through a vsecond winding of reley'39 to conductor 106.

35 is a key, the movehle-contacts of which are connected to conductors4'1 and 42 respectively, by whichkcy the central operator 7 may connecther telephone set 120 with the; calling sub scribers line forthe purposeof a s-- certngining the party with whom connectionis desired, and'bywhich said centrnl oper'stofrly wit a, subscriber evenif not cellerbbyanother may, should it be desired, also converse subscriber; The switchplugBO at one enl'l, ol the trunk has three plug contacts, one; con.nected by conductor to a. movable switch member ll-6 ofs key 34 smotherconnec teil j by' conductm (41m a second IXlOVitlJlG.Swillflll'member-117 of said key; and third contacteonnectedii cen ductor 7O whichextends inkling of" l current gen backcontact of an "armature 356 ofa lA conductor 80 extendsf-rom said I relay through 'a resistance- 34 I toconductor 69.[ Abrqnch- 1.18 lends conductor 76 to armature- 72 of relay37' to the Y responding to and current flows from condenser 36 tocontact 115 of'key.

'37. attract its nrmfl ure 54, n y -11), Ito corn erator 122 areconnected with back contacts adapted to .be engaged by-movableswitchmembers 116 and 117 respectively, upon .operation of the signaling key34.

127 is a brunch leading from conductor'lflfi 70 to armature 66 of -relay38;, said armature c normally retracted i-nto engagement with its backcontact, from WhlCl'I conductor. 77

leads to the front contactof armature :64

of a rel-ay 40-. A conductor 65 leads from the'front contest of armature66 to the back contect-of armature 64, and econductor 121- leads fromthe latter through signagllmfp said armature is' normal'lyretracted-into em 'gsgeme'nt with its back contact, from'which aconductor '1 19 leads through a signal lamp Asihas Already beenexplained,-the latter armature,- which isnormnl-ly retracted fromits'front contacts,- hesl a front contact connect'ed"tO conductorBQL vHaving thusfdeseribed the mechanism and circuits in their. nor-midinactive positions'in I which they are shown in the drawing-,1 will" nowdescribe the operation of the-system in 1 a call, initiated y; the.subsomber at substation l9by the removal of his through the electricalthroughelements 107- at this point thecurre'nt divides, the minor hook.Th removal e; i

the minor-portion through 101 und'windin'g lof 26y-continuing, the fullcurrent flows through elements .to'ground, energizing relays25 and2.6.'; Be-

lay 1.25 attracts its armature 50 end current flows j from 7 battery 13,.w on circuit.

147 through] element "107 *+"l0'9'-5Q- '11054r l11f;an(lwindings. fmagnet isfls u loeerosto the r r other. ole of the battery, g

s closed through-.inten deenergi zing'magnet 13 when circuit is open atinterrupter 15, thus alter/ 1 na telygenergizing andde'energizingffmagnet- 7 '11s 1,3 and 'stop ing the wipers 21,-,22 3r1d2-3 ing contacts 31,132 v trunk l'ine (e non-busy line being one, asmore'tu'llyexplainedv hereafter, n wh chthc armature 56'ofrelcy 37 restsngeinst tsba-pkontact, the position shown in the driiwing),

w'vihen'circuit is establishedfor'current from 1.

"-47 ti-u'ough' elements 107-=69-55 will one-winl'l ingof Teleyi37--306- back to. the battery, thus energizing relays 24 and cuit throughmegnet 13, thereby preventing fiuthersteppmg of wipers This'energizatloncf relayle causes it V interrupting the cm lay 24 also attracts itsarmature 58 and thereinto connection with conductors 102 and 103 matures66 and 67.

to wipers 21', 22, respectively, which wipers are now in electricalengagement with waiting contacts 31 and 32, respectively; thus path isfurnished for current from one pole 'of battery 47 through elements10769-85 and one winding of relay,384232-22- 103 48 -101 and winding ofrelay 2618- 1918'49-10221-3141-83 and the other winding of relay38106l08 to the other pole of the battery, thereby maintaining theenergization of relay 26 by a path of current difierent from that bywhich said relay was originally energized, and also energizing relay 38causing it to attract its ar- By the attraction of .armature 66 signallamp 45- is caused to glow by current from one pole of battery throughelements'10769121 and lamp 64 65'66127106108 back to the other pole ofthe battery; and by'the atj traction ofarmature 67 path is given forcurrent from. battery through elements 107- 69'1136768 and one windingof relay 3756' the other winding of relay 37 57 106 to the other pole ofthe battery, thus continuing the energization of relay 37 j v by a pathof current different from the path by which said relay was at firstenergized, as heretofore explained, thus also continuing the isolationof conductor '43 from armature 56 so long as this particular trunk isengaged, and thereby also isolating said conductor 43, its branchconductor 53 and waiting contacts connected with the latter conductor atthe automatic switches of other telephone lines, from the connectiontoone pole of the battery by way of armature 56, which connection isnecessary to permit the original energization of the relay 24 of anyother line which may institute a call;

' a busy test, to wit, that condition in which the relay 37 holds itsarmature 56 attracted against the front contact of 'said armature,

. I (particularly upon the testing contact 33) of is thusplaced upon thewaiting contacts e selected trunk, to prevent the automatic selection ofthat trunk by. the automatic i 1 switch of any other calling line. 0]

scribed above, by which energization of relay The completion of thecircuit last de- 37'is maintained, involves, as was seen, the engagementof armature 56 with its front contact, .which latter is connected toconductor 68 this contact originally resulted by movement of armature 56under influence of current over the previously traced circuit from onepole of attery 47107-6955 and one winding of relay 24-233356 one windingof relay 3757.'106- to the other pole of said battery. If at the instantthe armature 67 of relay 38 moves into engagement with itsfront contact,the armature 56 should happen not to be in engagement with its frontcontact, then armature 56 having fallen back into engagement with itsback contact will again close the circuit from conductor 43 through onewinding of the relay 37, thus again energizing the latter, causing it toattract its armature 56 against its front contact, and therebyestablishing the second above-traccd'path for energizing current ofrelay 37, which thereupon holds its armature 56 in engagement with thefront contact connected to conductor 68; this energizing circuit of' manet 37 will remain complete, to maintain t e busy test condition of thetrunk line, until said circuit is disrupted as hereinafter explained.

The energization of relay 24 and the consequent circuit from one pole ofbattery 47 through elements 107112-5960-58- one winding of relay2461-286263 Winding of relay 27 to ground (which cir-.

'cuit has already been explained as having energized relay 27 to attractits armatures 48 and 49), connects the test rings of switchboard jacks20 of the calling line 19, with battery 47 in such manner that a busytest will be received by the operator at any section of the multipleswitchboard when she tests at her section, the jack 20 of the callingline 19, such'testing being effected with a lug 30 in the mannerwell-known in switchhoard service. It will thus be seen that the act ofthe calling subscriber at 19 in lifting his receiver fromits'hook-lever, automatically eifects, by a rapid succession ofoperations, the connection of the calling line with a non-busy trunk,and the establishment of conditions whereby said calling line and thetrunk selected will both test busy making it impossible for any othercalling line to connect with said trunk during the maintenance of thebusy test condition established in the trunk, and also establishingconditions whereby said calling line will test busy at all sections ofthe switch-board. This act of the subscriber also causes lamp 45 toglow, notifying the central operator in charge of the particular trunkto which connection has been effected, that a calling telephone line hasbeen connected to that trunk. This condition will remain as long as thereceiver at substation 19 remains oif its hook-lever, and

until the central-office operator responds to the call.

' The central-station operator answers the call in the well-known way bydepressingher key .35, thereby connecting her telep one outfit 120 withthe calling subscriber s telephone over the following path: from theupper movable contact of key 35, elements 41 and 3631-21102-49181918- 2948103223242 and 36- to the lower movable contact of key 35 one side oftelephone line, and finding the line not busy tion 19 is on itshook-lever.

inserts her plug 30 in said jack. A circuit is thus completed from onepole of battery 47, elements 107--69- winding of relay 7 0-63- windingof relay 2'7-1()6-108 to the other pole of the battery. This circuitenergizes relays 40 and 27 the former attracting its armature 64,thereby opening the circuit which caused lamp to glow, and the relay 27attracting both, its armatures 4S and 49, thereby isolating line 18 fromits automatic switch equipment, notshown'. Relay 40 also attracts itsarmature 71, thereby' establishing path for current through lamp 46 bythe following elementsfrom one pole of battery 471076971119 and lamp467211876106108 to the other pole of said battery, thereby causing lamp46 to glow as a signal to the operator that the telephone-receiver atsubsta- The operator then actuates her key 34, thereby connectingsignaling generator 122 with the line of the called subscriber andringing the signal-bell at the telephone substation 19.

The central operator having released her ringing-key 34, and the calledsubscriber having removed his receiver from its hooklever, circuit isclosed for current from one pole of battery 47, through elements 1076973 and one winding of relay 3942r 11411774l8-19l8'751l6 115-4176 andthe other winding of relay 39- 106108-'-to the other pole of saidbattery; relay 39 is thereby energized and by attracting its armature 72opens the circuit through lamp 46 and extmguishesthe latter, thusindicating to the central operator that the called subscriber hasremoved his receiver to answer the call. Lamps 45 and 46 being thus bothdarkened, and the calling and called parties being connected forconversation, the central operator gives the connection no furtherattention until the glowing of those *lamps for discon-,

nection. 1 The conversation circuit between the calling and calledsubscribers may be traced by the following elements: from callingsubscribers telephone 19, elements 18-- 117-74-]8-through the telephone19 of the called subscriber18751 16-1 1 5 41 and 36-3l211024918 -back t0the telephone 19 of the calling subscriber. The sides of this connectionare connected to the respective poles of common battery 47 from one poleof said battery by elements 107-69-lrom which latterthere are two paths,one path by element 85 and one 75 winding of relay 38 to conductor 42 atone side of condenser 36, and the other path by element 73 and onewinding of relay 39 to conductor .42 at the other side of said comdenser. From the other iole of said battery the connection extends byelements 108- 106-irom which latter there are two paths, one by element83 and winding of relay 38 to conductor 41 at one side of condenser 36,and the other path by element 76 and wind- 35 ing of relay 39 toconductor 41 at the otherside of condenser 36. Conversation having beencompleted, the lianging up of the telephone-receiver at substation 19interrupts the circuit heretofore traced through the windings of relay39, thereby dccnergizing said relay, which releases its armature toagain close the previously traced circuit by which lamp 46 was caused toglow.

Upon the hanging up of the telephone receiver at substation 19, thecircuit previously traced through the windings of relay 38 1sinterrupted, thereby deenergizing said relay,

which releases its armatures, armature 66 acting to again establish thepreviously we traced circuit by which lamp 45 was caused to glow. Theopening of circuit at substation 19 breaks the circuit previouslydescribed as having continued the cnergization of relay 26, and therelease of armature 59 com letes apath -for currentlrom one pole of theattery 47 through elements 107]12' 59-78 and magnet 14-17 79106 108tothe other )ole-o'l said battery,

thereby energizing re ease magnet 14 (switch 110 17 being closed bytllOOl'fdlOllnfi-l position of automatic switch 10) and releasing themoving part of automatic switch 10, which is thereupon actuated by aspring 12 to return it to the position shown in the drawing. 11!) Uponreaching this normal position the pin 16 acts upon the moving part ofthe switch 17 to open the latter, thereby interrupting the circuit lasttraced above, and dencrgizing magnet 14'. The release of armature 59above referred to, also opens the circuit from said armature toconductor 60, by which. relays 24 and 27 were energized, therebydenergizing said relays. The hanging up of the receiver at substation 19therefore acts automatically to restore to their normal positions(illustrated in the drawing) all parts of the central ollice equipmentindividual to line 18. But following the replacerrmnt upon theirhook-levers oil the receivers of both the call- 120 switch-board jack ofthe called line.

this interval, the busy-test, preventing coning and called lines,whereby both lamps 45 and 46"are caused to glow as signals to thecentral statiOnoperator, a brief interval of time will'necessarilyelapse before the central operator removes her plug 30 from the Duringnection of other calling telephone lines with this particular trunkshould be maintained, otherwise confusion may result from connectingsuch a calling "line with a trunk whose plug is inserted in the" jack ofa telephone subscriber who is'not the one desired by the callingparty.The maintenance of the busy-test upon the trunk during this periodis animportant part of the present invention. At this stage of the operationthe deen'ergization of relay 38 has caused it to release its armature67, thereby breaking at that point the previously traced circuit bywhich the en'ergization of relay 37was continued; but the energizationof relay 37 is continued until removal of the plug by a circuit throughthe following elements, to witone pole of battery 4'710769-71--80' 44onewinding of relay 3757 106 108t0 the other ole of the battery. Thiscircuit may be ca led an auxiliary busytest circuit. The armature 56 isthus held outof contact with conductor 43, and continues the busy-testupon the trunk until this last-traced circuit is interru ted in the Imanner about to be described.

membered that the signal lamps 45 and 46- t will be reare now glowingbefore thecentral operator as a signal for removal of her plug inresponse to these signals said operator removes this plug, whereby relay27 is denergized releasing its armatures 48 and 49, which restoreconnection of line 18 with its automatic switch-equipment not shown.Removal of the plug also breaks the energizing circuit of relay 40,which, by releasing its armature 71, opens the circuit last traced aboveas energizing magnet 37, thereby permitting armature 56 to engage itsback-contact, thus restorin the trunk to its nonbusy condition amestablishing conditions whereby the automatic switch of any callingtelephone line may efiect connection with said trunk.

The auxiliary busy-test circuit referred to above attains anotherdesirableand necessary result in permitting the central operator,

attendant upon plug 30,- to use that plug to j communicate by means ofher key 35, with any telephone line for which no'call has beenreceived,without danger of interruption from a calling telephone line. This Iseffected by simply'inserting her plug 30 into a jack 20 of. the line ofthe subscriber with I whom she wishes to converse, which act results inthe energization of relay 40 and the completion of the auxiliarybusy-test circuit heretofore traced, the armature 56 being attracted,thereby placing upon the trunk the busy-test already referred to. Thec1rcu1t which energizes relay 40 also energizes relay 27, isolatingtelephone 19 from its auto- 'matic switch equipment in the mannerheretofore explained.

As will be understood from the preceding description, the automaticswitch 10 1n selecting a trunk continues the movement of wipers 21, 22,23, from trunk to trunk, until the wiper 23 makes contact with. awaiting terminal 33 from which circuit is' closed to one pole ofthe-battery by armature 56 oocupying the position shown in the drawing;

in other words, the movement of the wipers continues until relay'24 isenergized. The relay 24 also performs the function of connecting thetelephone line to a trunk by stop ping the moving wipers upon thewaiting contacts of a non-busy trunkv In view of these functions of therelay 24 it has been designated a testing connecting relay. The wiper23, by reason of its function, has been designated a testing wiper. Thewaiting terminal 33, by reason of its function, has been designated atest terminal.

The testing circuit may be referred to as being made up of two limbs, aprimary limb from battery through elements 10769 55 and Winding of relay24to wiper 23, and a secondary limb from waiting contact 33 throughelements 4356 winding of relay 37 57'106-108to battery; or throughelement 53 in addition if connection of theprimary limb be made withsome other waiting testing'contact in multiple with 33.

As already explained, the relay 27 per forms'the functions of thecut-off relay of the ordinary wholly manual switchboard, as it isolatesthe call-forwarding element from the line when the latter is connectedwith its call-receiving element. fore been. designated a cut-ofi relay,al-

though it has also the further function of connecting the line to theconductors 102 and T03 and through the latter to the trunk conductors 41and 42, thus completing the conversation circuit from the telephone 19to the trunk. In res ect to this latter function, relayv 27 may e calleda line connecting relay".

This relay has there tact of said testing relay by which circuit theenergization of said line relay; a trunk havenergization of said testingrelay may be continued independently of said testing wiper,substantially as described.

2. In a call distributing telephone exchange system, an automatic switchhaving a movable testing Wiper; waiting contacts adapted to be connectedwith by said wiper a source of current; a circuit connecting saidwaiting contacts to said source; means for isolating said contacts fromsaid source of current; a testing relay with its windings connectedbetween said source of current and saidtesting Wiper, and adapted to beenergized when said testing wiper engages a waiting contact connected tosaid source; and a local circuit controlled by an armature conact ofsaid testing relay whereby the enerization of said testing relay may becon tinued independently of the isolation of said engaged waitingcontact from the current source, substantially as described.

3. In a call distributing telephone exchange system, a telephone line;automatic selecting equipment connected with said line; a' plurality oftrunks; a connecting relay adapted to connect said telephone lineto oneof said trunks selected by the selecting equipment a testing relay; aseries line relay; a circuit including armature contacts of said seriesline relay; armature contacts and helical conductor turns of saidtesting relay, the Winding of said line connecting relay, and a sourceof electrical otential, whereby the energization of said line connectingrelay is attained upon the simultaneous energization of said series linerelayand said testing relay, substantially as described.

4. In a call distributing telephone exchange system, the combination ofa cut-off relay; ,2. line relay; a locking testing relay; and a circuitby which said locking testing relay controls the energization of saidcut-oft relay, and by which said locking testing relay is denergized. bythe deenergization of said line relay, substantially as described.

5. In a call distributing telephone exchange system, the combination ofa cut-off relay; a line relay; a testing rela a testing circuit by whichsaid testing re ay is energized 'upon engagement with a non-busy trunk;and a circuit by which the energization of said testing relay results inthe energiz'ation of said cut-ofi' relay and in the con tinuance of theenergization of said testing relay independently of the said testingcircuit, said latter circuit being subject torupture by thedeenergization of said line relay, substantially as described.

6. In a call distributing telephone exchange system, the combination ofa cut-off relay; a line relay; testing relay; a circuit by which saidtesting relay controls the energization of said cut-oil relay, and bywhich said testing relay is deenergized by the deing waiting contactsand a test circuit including one of said waitm g contacts and pro vidingfor the initial energization of said,

testing relay when said trunk is not in use, substantially as described.

7. In a call distributing telephone exchange system, the combination ofa cut-oil relay; a line relay; a testing relay; and a circuit by whichsaid testing relay controls the energization of said cut-oil relay, andby which said testing relay is denergized bythe deenergization of saidline relay; a trunk having a plurality of waiting contacts, including awaiting test contact; a testing .wiper adapted to make connection withsaid waiting contacts; a primary test-circuit limb extending from asource of current to said test Wiper, and including said testing relay,said source of current beingadapted to energize said testing relay whenan external circuit or secondary limb forms a closed circuit from saidtesting Wiper to said source; a secondary normally-closed testcircuitlimb extending between said waiting test contact and the source ofcurrent; and means whereby said secondary test-circuit limb is openedwhen said trunk is busy, substantially as described.

8. In a call distributing telephone exchange system, the combination ofa line relay; a testing relay; a primary test-circuit limb includingsaid testing relay; a trunk; a secondary test-circuit limb associatedwith said trunk and providing for the initial energization of saidtesting relay only when said trunk is not busy; and a circuit wherebysaid testing relay may be deenergized by the deenergization of said linerelay, substantially as described.

9. In a call distributing telephone exchange system, the combination ofa trunk having mult ple terminals for connection and multiple terminalsfor busy test; a relaf? (as 37) for causing said busy-test terminals togive a busy test; switching devices (as 30 and 20) tor connecting saidtrunk with a selected line; a relay (as 40) energized incident to theconnection of said trunk with a selected line; and a circuit whereby theener' 'gization of said latter relay (as 40) will cause the energizationof said former relay (as 37), substantially as described.

10. In a call distributing telephone, exchange system, the combinationof an automatic switch; a trunk having busy-test eonditionwhen the trunkis busy differing from to continue the energization of said testingchange system, the combination of an automatic switch; a trunk havingbusy-test con dition when the trunk is busy differing from its busy-testcondition when the trunk is non-busy; a testing relay; testing circuitsadapted to energize said testing relay upon connection with the non-busytrunk; armature contacts of said testing relay to interrupt the motionof said automatic switch; armature contacts of said testing relay tocontinue the energization of said testing relay independently of saidtesting circuits; and a line relay adapted to deenergize said testingrelay, substantially as described.

12' In a call distributing telephone exchange system, the combination ofan automatic switch; a trunk having busy-test condition when the trunkis busy differing from its busy-test condition when the trunk isnon-busy; a testing relay; testing circuits armature contacts of saidtestin relay to I ture contacts of said testing relay to inter- Y ruptthe motion of said automatic switch;

continue the energization of said testing;

relay independently of said testing circuits;

a cut-ofi relay; controlledby armature con tacts on said testing relay;and 'a line relay adaptedto denergize said testing relay, sub-'stantially as described.

Signed by me at Pittsburg, county of Al legheny, State of Pennsylvania,'in the presence of two witnesses.- n k SIDNEY HAND BROWNE.

Witnesses: i

A. ILMORAWEGK, Anon M. GODFREY.

